A number of systems have been developed over the years to satisfy the requirement of maintaining the temperature of the passenger cabin of modern day aircraft at a level that is comfortable to the passengers during the time the aircraft is parked. In such aircraft, the high density of passengers, the interior lighting, the large number of windows, and the heavily insulated fuselage all contribute to raising the temperature of the cabin of the parked aircraft to uncomfortable levels. Accordingly, it is necessary to provide a cooling system to lower the aircraft cabin temperature, even when the aircraft is parked in locations with relatively cool outside ambient temperatures.
One type of prior art system for cooling the cabin of a parked aircraft utilizes an on-board auxiliary power unit which is generally a small, jet-fueled turbine. The turbine, which is operated when the aircraft is parked, is used to power the on-board cooling system. During flight, the main engines power the cooling system.
Another type of prior art system for cooling the cabin of a parked aircraft utilizes one or more on-board air cycle machines, which are special-purpose heat pumps. These machines cool the cabin air when they are supplied with a source of high-pressure, high temperature air. During flight, the source of air is an on-board compressor driven by the main engines. When the aircraft is parked, a ground-based air compressor is connected to the aircraft to drive the heat pumps. This connection is made using a hose which links the compressor to a heat pump connector provided on the outer surface of the aircraft fuselage.
Yet another type of system for cooling the cabin of a parked aircraft utilizes a ground-based air conditioner unit, which provides cool air under pressure directly into the cabin air-conditioning duct system. This ground-based air conditioner, which may be fixed in location or portable, is connected to the parked aircraft using a flexible hose. This hose links the air conditioner to a connector, provided on the exterior of the fuselage, which communicates directly with the cabin ducts. In this mechanization, there is no need to operate the on-board cooling system when the aircraft is parked.
Of the previously described types of cooling system, the ground-based air conditioner unit is generally recognized as being the most energy efficient. Typically, prior art ground-based air conditioner units require from one-fifth to one-tenth the energy of those systems employing on-board auxiliary power units, and from one-half to one-fourth the energy of those systems employing on-board air cycle machines.
Even though ground-based air conditioner systems are generally more efficient than many other types of cooling systems, they still require large amounts of power for their operation. For example, electrically operated air conditioner systems for large commercial jet aircraft may require in excess of three hundred and fifty kilowatts of power for their operation. This is a serious concern in applications where the air conditioner unit is located proximate the outboard end of a passenger boarding bridge. In such applications, the air conditioner unit draws on the power that is supplied to the passenger boarding bridge, and thereby reduces the amount of power that is available during peak demand for other applications, such as auto-leveling, interior lighting, etc.
While conventional systems have been suggested which utilize ground based power supplies, the continuing problem exists of adapting such systems to the requirements of different sized aircraft. Presently, there exists a multitude of aircraft models and types, each with their own respective passenger carrying capacity and cabin configuration. In large part the cooling requirements for a preconditioned air unit are determined by the number of passengers being housed within the cabin being supplied with preconditioned air, as well as the internal air distribution network and the overall spatial dimensions of the cabin. It follows that a particular preconditioned air system designed for servicing a given number of passengers and cabin configuration may prove inadequate for servicing an aircraft having a significantly larger or smaller passenger capacity and cabin configuration.
It would be advantageous to provide a preconditioned air system that is adaptable to different operating requirements depending upon aircraft size, passenger load, ambient conditions, etc.